Method of making copper tubing



June 22, 1965 E. v. CRANE 3,139,938

METHOD OF MAKING COPPER TUBING Filed April 18, 1961 4 Sheets-Sheet 1 l EXTRUSION LUBSIFQATION OOMPACTS SINTERING COMPACTION FIG. I

BLENDING LUBRICANT INVEVTOR. EDWARD V. CRANE ATTORNEYS FIG. 3

June 22, 1965 E. v. CRANE METHOD OF MAKING COPPER TUBING 4 Sheets-Sheet2 Filed April 18, 1961 mvmron EDWARD V. CRANE mm 1, u on w. mm HH H HI Il I |.|.l V m llll I =l f A ow m/ T m. I n.\\ ov we 2 r N? w fi ats June22, 1965 E. v. CRANE 3,189,988

METHOD OF MAKING COPPER TUBING Filed April 18, 1961 4Sheecs-Sheet 3 8FIG. 8 Y 34 so 70 i 2 I 72 1| 4o 38 I2 22 73 A 5 3| 2o INVENTOR.v EDWARDV. CRANE ATTORNEYS June 22, 1965 E. v. CRANE 3,189,988

METHOD OF MAKING COPPER TUBING Filed April 18. 1961 4 Sheets-Sheet 4FIG. IO

. I2 I l l I k if INVENTOR. EDWARD v. CRANE BY UmmMT bfiniqk ATTORNEYSUnited States Patent 3,189,988 METHOD 0F MAKING COPPER TUEING Edward V.Crane, (Canton, Ohio, assignor to E. W. Bliss Company, Canton, OhioFiled Apr. 18, 1961, Ser. No. 103,868 17 Claims. (Cl. 29-4205) Thisinvention relates to forming tubular products from metallic powder. Moreparticularly, this invention relates to a method of blending andcompacting finely divided metallic powder into a green compact, removingimpurities from the green compact, coalescing the metallic particles,and, thereafter, forming a tubular article from the compact.

It is well known that copper, nickel, and other nonferrous metals may berecovered from scrap, low grade ores, and from liquors obtained duringbeneficiation procedures involving high grade ores containing thesemetals. The metal recovered from these various sources may beprecipitated in powder form having greatly varying particle sizes.Attempts to prepare flat shapes such as strips and bars from a greencompact to powdered metals have been generally successful. Fabricationof metallic particles into shapes such as tubing by conventionaltechniques of powdered metallurgy has not, however, proved satisfactory.One of the difiiculties in forming metallic powder into dense shapes,other than strips and bars, has been the inability to avoid theinclusion in the final product of excessive amounts of metallic oxidesformed by the readily oxidizable metallic powders. Another difficulty informing dense shapes is caused by the fact that compacts, heretoforeutilized, have been very dense and have resisted conventional metalforming techniques to convert them into shapes.

It is the general object of the present invention to provide an improvedmethod for forming metallic articles in a continuous manner frommetallic powder with the final article being substantially pure metal,extremely dense, and substantially oxide free.

It is another object of this invention to provied a method of blendingand compacting finely divided metallic powder to obtain a green compactwhich is sufiiciently dense, having a self-supporting shape, while atthe same time being sufiiciently porous to permit further operations foreffecting the removal of undesirable oxides.

It is a further object to provide a method for removing from the greencompact undesirable oxides, as well as impurities resulting fromadditives which may have been added to enhance the blending andcompaction of the metallic powder.

A still further object of this invention is to prepare a metallictubular article from a metallic compact by extrusion of the compact.

It is a still further object of this invention to provide a novelextrusion apparatus for forming the metallic tubular article.

Copper has been selected as an example of a metal which may be treatedaccording to this invention. Ferrous and other non-ferrous metals andmixtures of such metals may be converted from metallic powder toextruded shapes according to this invention, as will be obvious to thoseskilled in the art.. Other objects and advantages will become obvious tothose skilled in the 3,139,98 Patented June 22, 1965 art from a study ofthe specification taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a flow sheet illustrating the basic steps of formingmetallic tubing from powder according to this invention;

FIGURE 2 is a perspective view of the general structure of the type ofmetallic tubing which may be formed according to the method of thisinvention;

FIGURE 3 is a front elevational view, partly in section, of theextrusion apparatus of one type which may be used to form metallictubing from the compact;

FIGURE 4 is a front elevational view, partly in section, of theextrusion apparatus illustrating the general relationship of theapparatus and the compact before extrusion, and various shapes assumedby the compact before, during and at the end of the stroke of theextrusion punch, according to one embodiment of this invention;

FEGURE 5 is an enlarged view of the encircled portion of FEGURE 4illustrating the coaction of various parts of the extrusion apparatus;

FIGURE 5A is a view similar to FIGURE 5, but with the punch and mandrelomitted from the View;

FEGURE 6 is a perspective view of a portion of the metallic tube madeaccording to the extrusion apparatus illustrated in FIGURES 3 and 4;

FIGURE 7 is a front elevational view, partly in section, of theextrusion apparatus, illustrating the general relationship of theapparatus and the compact before extrusion, and various shapes assumedby the compact before, during and at the end of the stroke of theextrusion punch, according to another embodiment of the invention forextruding compacts in tandem;

FIGURE 8 is a front elevational view, partly in section, illustratingthe coaction of the extrusion punch with compacts arranged in tandem;

FIGURE 9 is a front elevational view, partly in section, similar toFIGURES 7 and 8 outwith the extrusion punch further along in theextrusion stroke;

FIGURE 10 is a front elevational view, partly in section, similar toFiGURE 8 but with the punch at the end of the extrusion stroke in thetandem arrangement of the compact; and

FIGURE 11 is a perspective view of the metallic tube formed according tothe embodiment of this invention illustrated in FIGURES 7-l0.

Referring to FIGURE 1, it will be seen that the first step of the methodaccording to this invention is to blend the metallic powder particlesprior to compaction. The purpose of this step is to uniformly mix themetallic powder, which is generally composed of minute particles ofvarying sizes, to obtain a particle mass having a uniform particledistribution. Preferably, the copper powder mass should have an averageparticle size of approximately 12.3 microns, although average particlesizes ranging from 10 to 12 microns have been found satisfactory for usein this invention. The use of an excessive percentage of copperparticles of less than 10 microns has been found undesirable becausetubes extruded from compacts formed of such powder have been found tocontain blisters and cracks. The increased blistering resulting from theuse of smaller than 10 micron size particles appears attributable to thegreater amount of oxides due to the greater surface area of theparticles. Cracking appears attributable to the presence of otherimpurities such as carbonaceous residues, which may be entrapped in thecompact when it is formed, and which are not readily removed bysubsequent procedures.

After the copper powder has been thoroughly mixed, a lubricant may beadded to the copper powder mass. The lubricant serves to reduce thefriction between individual particles during the compacting process, andto reduce the friction between the particles and the compaction diewalls. The lubricant should possess a relatively low melting point, andpreferably, be capable of melting under the influence of the heatgenerated during compaction. Metal soaps have been found to be excellentlubricants for this purpose. Such soaps include the stearate salts ofbarium calcium, zinc, lithium, and similar metals. A mixture oflubricants such as lithium stearate and Emersol 150 has been foundadvantageous according to a preferred embodiment of this invention. Thislubricant mixture is formed of 0.25% lithium stearate and 0.2% Emersol150 by weight of copper powder. Other lubricants such as zinc stearateand stearic acid may also be utilized, although each of these lubricantswhen used alone has been found less effective than the combination oflubricant materials mentioned above. In the event the lubricant, whenadded, causes lumping of the particles, the lubricantparticle mass maybe screened, as with a 30 mesh screen to break up or remove the lumps.

The thoroughly blended mass of copper powder and lubricant is then fedto a compaction press for the formation of the green compact. Anysuitable manual or automatic compaction press may be utilized for theformation of the compact. The compact utilized in forming the extrudedtube according to this invention is cylindrical in shape and has centralbore extending axially throughout the length of the compact. Theparticular dimensions of the compact, will, of course, vary with theextent to which the powder is compacted, and with the length of tubingdesired from each extruded compact. The term green compact, as hereused, refers to the compact formed from the metallic particles withinthe compaction apapratus.

The degree of compaction of the blended particle mass should besufiicient to form a self-supporting compact, but should not compressthe particles so closely together as to obtain substantially fulldensity. Preferably, the compact should be self-supporting, porous,uniformly dense, and approximately 80-90% of full density.

The next step in the method of this invention involves the removal ofimpurities from the green compact. These impurities comprise oxides ofthe metallic powder which are entrained Within the compact, lubricantmaterials added to aid in the compaction process, and small amounts ofother impurities residing in the powder mass and not removed during therecovery process. The removal of these undesirable components from thecompact may be accomplished either in one step or in two steps dependingon the size of the compact and the extent and nature of the impuritiescontained therein.

The two step procedure involves, first, a pre-burning operation for theremoval of the lubricant, which has been added to the copper mass toenhance the compaction process, and other volatile components. Thepro-burning of the green compact takes place in a furnace, or in anantechamber section of a furnace, heated to about 1200 F. through whichthe green compact is passed. The exposure of the compact to heat duringpre-burning should be approximately 15-30 minutes, and the heatingshould take place in an inert atmosphere. In the preferred form of thisinvention, disassociated ammonia is used as the atmosphere within theslow burning furnace. The slow heating to which the compact is exposedduring the preburning stage will cause substantially all of thelubricant materials to volatize and pass off as gases, leaving onlyminute quantities, if any, of residue lubricant materials,

or their chemical components, remaining within the compact.

The compact may then be subjected to sintering, the second step of thetwo step procedure, which functions to further remove the lubricantresidues, reduce the oxides which have been formed, and to coalesce themetallic particles. Sintering is preferably performed at elevatedtemperatures in the range of 1920-1950" F, in an atmosphere containingreducing gases and inert gas components to minimize the possibility ofoxidation of the metallic particles in the heated compact. The uppersintering temperature is just below the melting point of the metalliccopper and is sufliciently high to coalesce the particles within thecompact. The porosity of the compact permits effective removal of theundesirable oxides, because the reducing gases are able to permeate thecompact. The atmosphere may suitably be disassociated ammonia whichprovides hydrogen for reducing the oxides, as well as the nitrogen toact as the inert atmosphere for preventing oxidation during the.sintering stage. In pracice, it has been found desirable to introducethe gases near the end, or cooling section, of the furnace, and to passthese gases through the furnace counter-current to the feeding of thecompacts into the furnace. In this way, the heated compacts areprotected by the inert atmosphere while they cool, and at the same time,heat is imparted to the gases.

It can be seen that the pre-burning stage is, in effect, a mild form ofsintering. The pre-burning stage suflices to remove some of theundesirable components (as the lubricant materials), but is notsutlicient to perform all of the sintering functions of the sinteringfurnace. If the compact is small, preburning is generally not requiredbecause the sintering furnace is capable of removing the lubricantmaterials and the oxides in one step. Both steps are desirable when thecompact is of a relatively large size.

The sintered compact is next coated with a lubricant. This lubricant isplaced on all external surfaces of the compact, including the surfacesof the axial bore. This lubricant may suitably comprise an admixture ofone of the well known stearate lubricant materials, such as lithium andzinc stearate and stearic acid in a volatile solvent as benzene. Thesolvent should be sufficiently volatile to provide a substantially dry,lubricant coated compact between the time the lubricant solution isapplied and the lubricant coated compact is extruded. The use of asolution has the advantage of ease of application, and insures coatingall surfaces.

A general arrangement of the extrusion apparatus (according to one formof this invention) found suitable for forming a tube, such as 2 shown inFIGURE 2, is shown in FIGURE 3. The apparatus comprises a punch 10having an axial bore 12 which houses mandrel 14. The punch is preferablymade of a sintcred carbide having a substantial cobalt content, in orderthat it may withstand the force to which the punch is subjected duringthe extrusion operation. The punch has a slightly convex face 16 to aidin centering the punch against the compact to be extruded. The punchalso has an undercut portion 1% to form a lip 20 for the purpose ofpinching off any flash which may extrude backward around the face of thepunch, as will be more fully described hereinafter. The mandrel 14 maybe made of substantially the same material as punch 10, or of anelectrolized high speed steel, lapped lengthwise. The mandrel 14- has atip 15 which is of a smaller diameter than the body of the mandrel.

Punch 10 has a conical portion 22 which is adapted to be grasped by thepunch supporting elements of the ram of the press. A socket 24 is formedin conical portion 22 to accommodate the thickened end 26 of mandrel 14for firmly seating the mandrel. A pressure plate 28 abuts against theback face of the punch and mandrel as shown to spread or distribute loadintensity. The punch may be securely fixed to the ram 31 (see FIG. 8) ofthe press and aligned with the die opening by means of a suitableretaining rings 30 and 32. It should be understood that the details forsecuring the punch to the ram 31 form no part of this invention, and anysuitable arrangement may be utilized so long as the punch and mandrelare firmly secured to the ram and aligned with the die opening. Itshould also be understood that the mandrel 14 may be integral with thepunch 16, or, preferably, may be a separate element removably secured tothe punch as described.

The die holder 34 is provided with a carbide or hardened steel insert36, both being provided with a bore 38 extending through the insert 36and the die 34. The hardened insert is preferably made of sinteredcarbide in order to withstand the extrusion forces. The hard insert ornib 36 has a contour 40 formed therein. The angle ,8 is the includedangle of the contour and preferably should be between about 110 to about150. The included angle of this contour is an important aspect of thisinvention, because too great an angle imposes excessive tensile strainson the mandrel 14 during extrusion, while too shallow an angle resultsin lapping of the ends of successive extruded tubes so that the tubeshang together. Bore 38 is slightly divergent in that it has acompensating slight taper outwardly from the entry end adjacent the nib36 toward theexit end of the bore.

Secured to the face of the die is a container 42 provided with ahardened insert or liner 44, with the bore 46 of the container axiallyaligned with the mandrel 14 and with the bore 38 provided in die 34 andthe insert 36. Bore 46 is slightly convergent in that it has a slightcompensating taper inwardly from the end adjacent the punch toward thenib 49. The tapering of bores 38 and 46 is best seen in FIG. 3. Theposition of the punch with respect to the container and die at thebeginning of the stroke is shown in FIGURE 3.

An annular stripping groove 41 (see FIGS. 3 and 5A) is formed at thejunction of the liner 44 and the die insert 36. The stripping groovecooperates with the punch lip 29 to shear off that portion of thecompact which may be forced behind the punch face 16 during extrusion,as shown in FIG. 5. The stripping groove also serves to keep thecompressed butt end 62 of the compact from being pulled out of the dieon the mandrel 14, as will be more fully understood from the descriptionof the extrusion process given below.

In the operation of the extrusion apparatus, a compact 43 (see FIG. 4)is fed into position opposite the bore 46 of liner 44 with the bore 54of the compact axially aligned with the mandrel 14. Preferably, the dieshould be heated prior to commencing extrusion in order to facilitatethe extrusion process. Any heating means associated with the die may beused, as is well known to those skilled in the art. As the punch movestoward the die (from left to right in FIG. 4) the tapered tip of mandrel14 will enter the bore 5% of the compact 48. As the punch and mandrelcontinue to move forward, the compact 48 is caused to enter thecontainer and to occupy a position shown at 52. Continued forwardmovement of the punch and mandrel will compress the compact to the formshown at 54. In compressing the compact from 52 to the position at 54,the punch has in effect increased the density of the compact fromapproximately 80% to substantially 100%. With further movement of thepunch and mandrel, the mandrel will enter the die bore 38, and the punchwill force the compact into the contour 40 of the die to extrude thecompact into the tube 60. At the end of the forward stroke of the punchand mandrel, the compact has a substantially conical butt end portion 62residing within the nib 36 of the die, with the balance of the compactextending through and beyond the die in the form of the extruded tube66. The stroke of the punch and mandrel is of such length as to preventthe punch from being bottomed in the die, i.e., with the punch face incontact with the die insert 36, to avoid damage to the punch or diemembers (see FIG. 5). The punch and mandrel are then withdrawn, duringthe return stroke of the press, and when the punch reaches the end ofits stroke, another compact 48 is fed into the position shown in FIG. 4.The forward stroke of the punch and mandrel will then feed this compactinto the container, will force it against the conical portion 62remaining in the nib of the die, and will compress this second compact.Upon compression of this second compact, continued forward movement fothe punch and mandrel will force the conical residue 62 through the dieto complete the extrusion of the first compact. The second compact willthen be extruded by the continued forward movement of the punch andmandrel until it is substantially entirely extruded with the exceptionof a conical residue remaining in the nib of the'die.

At the end of the forward stroke of the punch and mandrel, the punchface 16 abuts against butt end 62, as shown in FIG. 5. As extrusion ofthe compact proceeds during this forward stroke, a portion of thecompact adjacent the punch face will flow into the stripping groove 41,and a small amount of the compact may be forced between the punch lip 20and the bore 46, as shown at 47 in FIG. 5. When the punch is withdrawnduring the return stroke, the stripping groove 41 will serve to preventthe butt end 62 from coming out of the die on the mandrel, and theshoulder 49 of the stripping groove will coact with the punch lip 20 toshear off the portion 47 which may have been forced around the punch toproduce a substantially burr free butt end, as shown in FIG. 5A.

It will be readily understood that one tube is extruded for each strokeof the press. This follows, because one stroke substantially extrudesall of one compact, and the next succeeding stroke extrudes the conicalresidue of the first compact, if any, and substantially all of thesecond compact, as described above.

The tube 60 which has been extruded according to the embodiment is shownin FIG. 6. It will be noted that the tube has a slight mark 64 someditsance from the left end of the tube. This mark is in the form of aring, indicated at 64, of a slight offset or difference in diameter dueto thermal shrinkage, without, however, any appreciable difference inthe Wall thickness of the tubing.

The basis for the formation of this ring will now be explained. As shownin FIG. 4, the compact is approximately 75% extruded during the forwardstroke of the punch and mandrel. At the neck 66 (see FIG. 5) of theconical portion 62 remaining in the nib 36 of the die, there is atemperature differential. The extruded tube 60 to the right of this neckis at a very high temperature, being in the nature of approximately 800F. to 1000 F. The substantially conical butt end 62 remaining in the nibof the die cools quickly to a lower temperature resembling thetemperature of the die insert 36. This difference in the temperatureresults in a lesser shrinkage of the cooler butt end as it is extruded,and accordingly leaves the ring offset 64 at a point corresponding tothe orifice 66. Although the offset ring is not reflected in a varyingwall thickness or strength of the extruded tube, it does present aphysical feature visible to the naked eye on the external surface of thetube.

, According to another embodiment of this invention, extrusion isperformed under such conditions as to shift the ring 64 to an endposition where it will be removed in trimming, without in any wayvarying the quality of the tube extruded from the compact.

eferring to FIG. 7, there is illustrated an embodiment which utilizestwo compacts in tandem within the container. The punch and mandrelutilized in this embodiment are sustantially the same as thoseillustrated in FIG.

3, with the exception that the body of the mandrel 72 is significantlylonger than mandrel 14, in order to be capable of passing through twocompact elements in tandem. Mandrel 72 also has a tip 15 which performsthe same functions as described above. Similarly, the container 7 7i),and liner 73 according to the embodiment of KG. 7, are substantiallywider than container 42 and liner 44 shown in FIG. 4, in order to housethe two compacts in tandem. The die and die inserts are the same asthose illustrated in FIG. 4.

In the start up of the process according to the embodiment of FIG. 7,the punch 10 and the mandrel '72 are in their retracted position, thatis, away from the container and die. The die container 7% contains onecompact. For purposes of illustration, the compact adjacent the face ofthe die insert 36 is designated B, and the compact furthest from the dieface, and between the compact B and the punch and mandrel, will bedesignated as A. At the start of the extrusion operation, compacts A andB are of the same size and shape, both having the same shape as compactA. As the punch and mandrel move toward the container and die during thefirst stroke of the press, the face of the punch will, contact the faceof compact A, feed the compact into the die container, force compact Aagainst compact B, and will compress both compacts A and B. Furthermovement of the punch will force compact B into the nib of the die andfully extrude compact B. In the tandem arrangement of compacts, thefirst stroke of the punch and mandrel serves to compress the twocompacts within the container, such that a portion of compact B extendsto or slightly into bore 38, with the face of the compact within the nibof the die assuming the configuration of the nib. During the nextsucceeding stroke of the punch, the force applied against compact A istransmitted through compact A to compact B, completely extruding compactB into a tube through bore 38 of the die. At the end of the secondstroke, the die container 70 houses a compressed compact A which has aface adjacent the nib of the die conforming to the contour at of thenib. With the container housing one compact which is ready to beextruded, the sequence of operation of the embodiment utilizing compactsin tandem may be more readily explained.

Referring to FIG. 7, there is illustrated a compact B housed within thecontainer 70 with a portion of the compact extending to or slightly intothe die insert 36 such that a small portion of the compact may beextruded into the form of a tube :as at 74. While the punch and mandrelare in the return stroke position, as shown in FIGURE 7, a compact A,similar to compact 48, is fed into position opposite the bore 71 ofcontainer 70, with the bore of compact A axially aligned with themandrel 72 and bore 38 of the die. Forward movement of the punch andmandrel will feed compact A into the container 70 such that compact Aassumes the position A within the container. The arrangement of thepunch, mandrel and compacts A and B at this point of the extrusionoperation is shown in FIG. 8. Continued movement of the punch will causecompact A to abut against compact B, with the face of the compact (A)adjacent the face of the punch assuming the configuration of the face ofthe punch, and the face of compact A adjacent compact B assuming thecontour of contact B as shown in FIG. 9. As the punch and mandrelcontinue to the end of the stroke, compact B is completely extrudedthrough the die to form a tube 76 and compact A assumes the positionformerly occupied by compact B, as shown in FIG. 10. The punch andmandrel are then retracted and the apparatus is in position to receiveanother compact to repeat the extrusion of the compacts in tandem.

As it will be readily understood, two compacts may be placed within thecontainer 70 at the very beginning of the extrusion operation. However,once extrusion according to this embodiment continues, there will be onenew compact and one compressed compact within the container at thebeginning of the punch stroke, and only one compressed compact in thecontainer at the end of that stroke. The stroke of the punch is of alength required for completely extruding one compact and to 55 forcingthe second compact into the position formerly occupied by the extrudedcompact.

It will be noted that the extruded tube '76 (PEG. 11), has a slight mark65 substantially at the end of the tube, as distinguished from the mark64 shown on the tube in FIG. 6. Mark 635 is caused by substantially thesame differential shrinkage phenomena which forms the mark in the tubeaccording to the embodiment illustrated in PEG. 4 However, the mark asin the tube of FIG. ll is shifted to the end of the tube, because asnoted in PEG. 7, the compact (compact B) is only slightly extrudedduring the first stroke of the punch. For that reason, only a very smallportion of the extruded length of the tube is at a higher temperature,whereas the greater portion of the compact is Within the die, andconsequently, at the lower temperature. The tube extruded according tothe tandem arrangement of this invention permits the mark to be locatednear the end of the tube, such that when the tube is trimmed, the markis removed without substantially affecting the length of the extrudedtube. In this way, an extruded metallic tube may be obtained which hasno visible marking, either internally or externally, making it suitablefor those uses in which a slightly offset diameter is undesirable.

During the extrusion of compacts in tandem the mandrel tip performs animportant function in reducing the impact load on the extrusionapparatus. As the tip passes through the compact and the face of thepunch forces the compact into the contour 40 of the die during the startof the extrusion, the extrusion ratio will be relatively low because ofthe narrow mandrel tip. As extrusion continues, the extrusion orificewill be controlled by the difference between the bore diameter 38 andthe diameter of the body of mandrel 14. The forward end of the tubewill, as a result of the mondrel tip, have a slight thickening evidenceby a reduced internal diameter as at 30 (see FIG. 9) due to themomentarily larger orifice at the start of extrusion. This thickenedportion may be trimmed oif, if so desired. The mandrel tip, bycontrolling the change of extrusion orifice, eliminates the high peakload, encountered in extruding metal at the start of extrusion, if anattempt were made to achieve the maximum reduction at the very start ofthe extrusion.

Tubular articles formed according to the process of this invention havebeen found to possess properties superior in many instances to tubingextruded from billets of the metal. For example, a copper tube extrudedaccording to this invention has been found to have finer grain size andhigher tensile strength characteristics after annealing, than a tubemade from commercially available copper metal. Copper tubes extrudedfrom a compact, and annealed, possess a tensile strength of between35,000 psi and a yield strength of between about 13,000 to 14,000p.s.i., whereas commercially available tubes prepared, for example, fromDHP copper (following ASTM Specification 13-75) and annealed in the samemanner as the tubes formed according to this invention, possessed atensile strength of about 28,000 p.s.i., and a yield strength of about9,000 p.s.i. Tests for obtaining the above values were carried out usingconventional test equipment, following accepted ASTM procedures. Inaddition, the copper tubes made according to this invention retain thefine grain structure even after annealing. On the other hand, the grainsof tubes made from commercially available copper grow as a result of acoarser grain annealing.

Although this invention has been particularly described with respect toextrusion of copper compacts, it should be readily understood that theinvention is not limited thereto, but encompasses other non-ferrousmetallic compacts. Accordingly, the temperature ranges given, particlesize distribution, lubricant materials, time intervals, for example, areto be considered as illustrative and not in a limiting sense. Similarly,the invention is not limited to the specific apparatus disclosed, as anysuitable extrusion apparatus, feeding mechanism, compaction apparatusmay be used to achieve the objects of the invention, Whether by acontinuous operation or otherwise.

What is claimed is: 1. A method of preparing and extruding a sinteredshape adapted for use in an extrusion press to form a wrought metallicobject substantially 100% dense comprising the steps of:

providing a powder of a ductile metal having a limited number ofparticles less than microns and having an average particle sizedistribution in the order of 12 microns;

mixing a quantity of lubricant in said powder to lubricate the particlesand to form a lubricant-powder mixture having a substantially uniformpowder size distribution;

compacting the lubricated particles to form a porous green compacthaving a uniform density in the order of 18% of full density butsubstantially less than 100% dense;

sintering said green compact in a reducing atmosphere at a sinteringtemperature for said metal powder and for a period of time suificient tocause inter-particle bonding, the rate of heating being such as to firstvolatilize the lubricant whereby When the sintering temperature isreached substantially all of said lubricant is removed; and

extruding the sintered shape at an extrusion pressure capable of furthercompressing it to full density whereby the wrought object formed is freeof pin holes or internal voids.

2. The method as set forth in claim 1 wherein said lubricant-powdermixture has an average particle size to substantially pass through astandard 30 mesh sieve.

3. The method as set forth in claim 1 wherein the metal powder is copperand the sintering temperature is about 1900 F.

4 The method as set forth in claim 1 wherein said lubricant is anorganic composition at least one constituent of which includes lithiumstearate and has a melting point sufficiently low to fuse under theinfluence of heat generated in compacting the lubricated particles.

5. The method as set forth in claim 1 wherein said reen compact has adensity of approximately 80% to 90% of full density.

6. The method as set forth in claim 1 wherein the metal powder used ispredominantly of copper and said green compact is heated slowly to afinal sintering temperature of about 1900 F.

7. The method as set forth in claim 6 and comprising in addition thestep of preheating said green compact for about 30 minutes to about 1200F. in an inert or reducing atmosphere so as to remove substantially allof said lubricant prior to sintering.

3. A method of preparing and extruding a sintered annular compactadapted for use in an extrusion press to form wrought tubingsubstantially 100% dense comprising the steps of:

providing a powder of a ductile metal having a limited number ofparticles less than 10 microns and having an average particle sizedistribution ranging around 12 microns;

mixing a quantity of lubricant into said powder to lubricate theparticles and to form a lubricantpowder mixture having a substantiallyuniform powder size distribution, said lubricant having a melting pointsufficiently low to fuse under the influence of heat generated duringcompaction;

compacting the lubricated particles to form a porous annular greencompact having a uniform density in the order of 80% of full density butless than 100% dense;

sintering said green compact in a reducing atmosphere at a sinteringtemperature for said metal powder and for a period of time sufiicient tocause inter particle bonding, the rate of heating being such as to firstvolatilize said lubricant so that when the sintering temperature isreached substantially all of the lubricant has evolved leaving a puresintered compact for use in said extrustion press; and

extruding said compact at an extrusion pressure capable of furthercompressing it to full density whereby the tubing formed is free of pinholes or internal voids. 9. The method as set forth in claim 8 in whichtubing is formed by extruding a plurality of said compacts fedsequentially to the press by the steps of:

partially extruding a first compact by a direct application of theextruding force thereto, the stroke of said press being restrained so asto leave an annular butt portion of the compact in the press compressedto full density; recycling the press and feeding a second compactthereto between the extrusion force and butt portion;

extruding the butt portion by first compressing the second compact tofull density and thereafter transmitting the extrusion force through itto said butt portion; and

partially extruding the second compact so as to leave an unextruded andfully compressed annular butt portion in the press at the conclusion ofeach cycle.

10. The method as set forth in claim 9 comprising deforming said annularbutt portion between a punch and mandrel and the threshold of theextrusion orifice of the press so that it is conical in shape and has aconical surface facing the direction of application of said extrusionforce against which the second compact abuts.

11. The method as set forth in claim 1'0 wherein the metal powder ispredominantly copper and the surface of the butt portion facing thethreshold of the extrusion orifice is at an included angle of at leastbut less than 12. The method as set forth in claim 10 comprising inaddition relieving the impact extrusion pressure at the initialapplication of the extrusion force by temporarily increasing the size ofthe extrusion orifice so as to extrude a slightly thicker walled tube atthe start.

13. The method as set forth in claim 10 comprising in addition deforminga peripheral part of said butt portion into a recess circumjaoent thepunch and continuing application of the extrusion force causing areverse extrusion thereof into an undercut portion of the punch andshearing said peripheral part from the butt portion leaving asubstantially burr free butt portion for reception of successivesintered compacts upon retraction of the punch.

14. The method as set forth in claim 13 wherein the radial edge of saidbutt portion has a smooth curvature in an axial direction and isretained in said recess to prevent said butt portion from beingdislodged with the Withdrawal of said punch and mandrel.

15. The method as set forth in claim 8 in which tubing is formed byextruding a plurality of said compacts fed sequentially to the press andcomprising;

feeding first and second annular compacts in tandem relationship intothe press such that the second compact is behind the first;

compressing both compacts to full density and thereafter applying theextrusion pressure to said second compact to completely extrude thefirst compact, the press stroke being restrained such that the juncturebetween said compacts will be adjacent the threshold of the extrusionorifices at the end of the stroke;

recycling the press and feeding a new compact thereto behind the fullycompressed second compact; completely extruding the second compact byfirst compressing said new compact to full density and theremasses 1 1after transmitting the extrusion force through it to said second compactwhereby each new compact will take up the position vacated by itspredecessor with each successive application of the extrusion force soas to always leave a fully compressed compact in the press at theconclusion of each cycle.

16. The method as set forth in claim 15 in addition comprising relievingthe extrusion pressure at the initial application of the extrusion forceby temporarily increasing the size of the extrusion orifice so as toextrode a slightly thicker walled tube at the start.

1'7. The method as set forth in claim 15 comprising deforming the fullycompressed compacts so as to form a orifice having an included angle ofat least 110 but less than 180.

References Cited by the Examiner UNETED STATES PATENTS 2,001,134 5/35Hardy.

2,290,734 7/42 Brassert 270-10 2,679,932 6/54 Burns 270-10 2,879,8873/59 Hawtin 207--10 2,954,869 10/60 Swanson 2072 2,967,613 l/61 Ellis etal. 2072 3,075,244 1/63 Glenn 29-420 X WHITMORE A. WILTZ, PrimaryExaminer.

conical surface adjacent the threshold of the extrusion 15 PTPUIWD HEANES IR Examiner ,,.s1 Le. 1

1. A METHOD OF PREPARING AND EXTRUDING A SINTERED SHAPE ADAPTED FOR USEIN AN EXTRUSION PRESS TO FORM A WROUGHT METALLIC OBJECT SUBSTANTIALLY100% DENSE COMPRISING THE STEPS OF: PROVIDING A POWDER OF A DUCTIBLEMETAL HAVING A LIMITED NUMBER OF PARTICLES LESS THAN 10 MICRONS ANDHAVING AN AVERAGE PARTICLE SIZE DISTRIBUTION IN THE ORDER OF 12 MICRONS;MIXING A QUANTITY OF LUBRICANT IN SAID POWDER TO LUBRICATE THE PARTICLESAND TO FORM A LUBRICANT-POWDER MIXTURE HAVING A SUBSTANTIALLY UNIFORMPOWDER SIZE DISTRIBUTION; COMPACTING THE LUBRICATED PARTICLES TO FORM APOROUS GREEN COMPACT HAVING A UNIFORM DENSITY IN THE ORDER OF 18% OFFULL DENSITY BUT SUBSTANTIALLY LESS THAN 100% DENSE; SINTERING SAIDGREEN COMPACT IN A REDUCING ATMOSPHERE AT A SINTERING TEMPERATURE FORSAID METAL POWDER AND FOR A PERIOD OF TIME SUFFICIENT TO CAUSEINTER-PARTICLE BONDING, THE RATE OF HEATING BEING SUCH AS TO FIRSTVOLATILIZE THE LUBRICANT WHEREBY WHEN THE SINTERING TEMPERATURE ISREACHED SUBSTANTIALLY ALL OF SAID LUBRICANT IS REMOVED; AND EXTRUDINGTHE SINTERED SHAPE AT AN EXTRUSION PRESSURE CAPABLE OF FURTHERCOMPRESSING IT TO FULL DENSITY WHEREBY THE WROUGHT OBJECT FORMED IS FREEOF PIN HOLES OR INTERNAL VOIDS.